The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A typical multi-speed automatic or hybrid transmission uses a combination of torque transmitting devices, such as clutches or brakes, to achieve a plurality of forward and reverse gear or speed ratios as well as a Neutral and a Park. Selection of speed ratios is typically accomplished by a microprocessor transmission control module that employs various vehicle parameters, for example vehicle speed, and various driver input signals, for example accelerator pedal position, to select the appropriate speed ratios. The transmission then engages a combination of the toque transmitting devices to provide the desired speed ratios.
In order to engage the torque transmitting devices, a typical automatic or hybrid transmission includes a hydraulic clutch control system that employs a hydraulic fluid to selectively actuate pistons within the torque transmitting devices and to provide lubrication to the device. Actuation of a piston in turn engages the torque transmitting elements (i.e., friction discs and metal plates) within the torque transmitting device.
Hydraulic or lubrication fluid within the torque transmitting device must drain out to return to a sump. Typically, hydraulic or lubrication fluid drain features are incorporated in the face of the piston. However, due to the large apply area of the piston, high stresses can develop in typical drain features due to the drain features interrupting the continuous hoop of the apply face of the piston. Accordingly, there is a need in the art for a torque transmitting device that operates effectively and smoothly that reduces the stresses developed on the piston while providing effective hydraulic or lubrication fluid drainage to the sump.